Chlamydia trachomatis has been recently implicated as the causative agent for several disease syndromes whose etiologics were previously unknown: non-gonococcal urethritis, epididymitis, acute proctitis, cervicitis, salpingitis, neonatal inclusion conjunctivitis and pneumonitis. The frequencies of these infections indicate a clear need for improved diagnostic methods and disease prevention. This project is concerned with those two long-term objectives by first defining the immunologic properties of components on the surfaces of C. trachomatis organisms in an attempt to understand the antigenic properties of these immunological accessible macromolecules. Current work is focused on the major outer membrane protein (MOMP) as an antigen that may have application in the future development in both the immunodiagnosis and immunoprophylaxis of C. trachomatis infections. The MOMPs of several C. trachomatis strains are being purified by preparatory sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and characterized both antigenically and structurally.